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cmakefilecc

Does GNU make implicitly compile .c files to .o files?

Noob question. I want to compile bar.c with object file foo.o to an executable bar. I have this in a Makefile:

bar: foo.o 
    cc bar.c foo.o -o bar

I run $ make -n and get :

cc    -c -o foo.o foo.c 
cc bar.c foo.o -o bar

I'm looking at the first line of output cc -c -o foo.o foo.c. I didn't write an explicit rule compiling foo.c to foo.o. Does make do this implicitly when it sees a .o target?

Solution

  • Yes, GNU make has a catalog of built-in rules:

    Compiling C programs
    n.o is made automatically from n.c with a recipe of the form ‘$(CC) $(CPPFLAGS) $(CFLAGS) -c’.

    Linking a single object file
    n is made automatically from n.o by running the linker (usually called ld) via the C compiler. The precise recipe used is ‘$(CC) $(LDFLAGS) n.o $(LOADLIBES) $(LDLIBS)’.

    so you could just write:

    bar: bar.o foo.o